Messages in this thread | | | Date | Wed, 04 Feb 2004 16:24:22 -0500 | From | Jeff Garzik <> | Subject | Re: [BUG] unsafe reset in ac97_codec.c |
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Liam Girdwood wrote: > /* probing AC97 codec, AC97 2.0 says that bit 15 of register 0x00 > (reset) should > * be read zero. > * > * FIXME: is the following comment outdated? -jgarzik > * Probing of AC97 in this way is not reliable, it is not even SAFE !! > */ > codec->codec_write(codec, AC97_RESET, 0L); > > > IMO, this is unsafe because it can also reset the codec into it's > default power state which can be "power down". This is not normally a > problem for PC's, but some battery powered devices have the default > codec state as "power down" to conserve power. > > Was this introduced as a workaround for some buggy device ? > If no one objects I'll submit a patch.
In general it's important for Linux to be able to reset a device reliable. Where in Other Operating Systems one must reboot the computer, Linux users can just re-load the driver quite often.
So I think there are two comments here:
* I can certainly see -probing- being unreliable (but not necessarily reset)
* If the default state for some devices is power-down, the driver should be aware of that -anyway-, and we should power up on startup or on-demand.
Jeff
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